Ava Jenkins, Liam Nash, Zoe West, Natalia Traxel, May Webber, Richard Wademan.
Introduction Inspiration for this experiment was drawn from paper "Polymorphism in Cepaea: A Problem with Too Many Solutions?" by S.Jones et al[1]. In this paper, Jones discusses how difficult it is detecting which genetic driving force is primarily behind variation and gene frequencies in one or more populations, with all (normally) being present in differing amounts. During this experiment we were originally attempting to solve a number of problems. Namely:
To determine the most prevalent reason for polymorphism in a snail population
olymorphism distribution is maintained by Selection, Gene Flow, Drift, or Mutation. Which of these forces play the biggest role in determining a polymorphic population.
To determine if the effects of selection and mutation are negligible compared to drift and gene flow.
To become familiar with the set up and processing of a sampling design, appropriately analysing test results to eventually draw conclusions from a chi-squared test.
Polymorphisms are the presence of different phenotypes existing in the same species in the same population. We are looking at distribution of polymorphic
types based on environment, and how the distribution is related to gene flow, selection and genetic drift in the snail species Cepaea nemoralis.
However, after reviewing Jones' paper, we decided to study on determining solely whether the presence of polymorphisms in Cepaea nemoralis and environment-type had any visible correlation as a precursor to determining whether this implied selection was evident in this species, and if there was measurable gene-flow of the selected-for polymorphisms between populations in different habitats. Glossary of technical terms and their definitions: Polymorphism - the occurrence of different forms among the members of a population or colony, or in the life cycle of an individual organism. Subadult - an animal that is not fully an adult. Any snail that is a juvenile and doesn’t meet the size requirement to be classified as an adult is considered a subadult. Genetic drift - the change in the frequency of a gene variant (allele) in a population due to random sampling. Gene flow - the transfer of alleles or genes from one population to another. Migration into or out of a population may be responsible for a marked change in allele frequencies (the proportion of members carrying a particular variant of a gene). Hypotheses: Our null hypothesis is: There will be no correlation between the different environment type and polymorph types.
With the alternative being: There will be a correlation between different environment types and different polymorph types. Reasoning: As we are solely looking at distribution of snail polymorphisms between different environments, we are not testing for cause and effect - making testing
in the same environment multiple times less relevant. To reduce variables we are keeping our sampling locations on the same altitude along
a single transect. Our peripheral spots are completely within the given environment (forest and bush) with the following locations being just at
the periphery of this environment. The centre two are in between, completely outside of each environment, in grassland. This will construct a
gradient of samples between two separate locations.
Our original sample designs were as follows:
Sample Design 1.
Sample Design 2.
Reason for changes made
We felt there was not enough replication in the original design and it is not representative of the area as a whole, it leaves too much open
to chance as it covered only a small area of the habitat. Our original model would provide a more "in depth" view of the gradient of gene flow
as the sampling sites on the periphery and within each Wood and Bush area. We feel limited by the small number of sites that we will be able to
sample from in the time given so we have chosen to sample at a constant altitude across the entire area with replication in all three habitat types.
Sample Design 3.
Reason for changes made
First we decided to reduce the number of variables by only sampling 2 habitats and increasing repetition of the conditions of the measurements.
We hoped our investigation could compare phenotypes, grass samples are near forest samples, to investigate gene flow prevalence across the habitats.
Repetition of these conditions x3. Justifying the method
Our method was to collect samples in two different habitats at sites which were close to each other where gene flow is possible. We did this because
we wanted to investigate the distribution across two different habitats to assess the possibility of gene flow having a considerable effect on the distribution
of polymorphisms. We replicated the samples three times for each habitat to produce a more representative sample size and reduce experimental error.
Introduction
Inspiration for this experiment was drawn from paper "Polymorphism in Cepaea: A Problem with Too Many Solutions?" by S.Jones et al[1]. In this paper, Jones discusses how difficult it is detecting which genetic driving force is primarily behind variation and gene frequencies in one or more populations, with all (normally) being present in differing amounts. During this experiment we were originally attempting to solve a number of problems. Namely:
- To determine the most prevalent reason for polymorphism in a snail population
- olymorphism distribution is maintained by Selection, Gene Flow, Drift, or Mutation. Which of these forces play the biggest role in determining a polymorphic population.
- To determine if the effects of selection and mutation are negligible compared to drift and gene flow.
- To become familiar with the set up and processing of a sampling design, appropriately analysing test results to eventually draw conclusions from a chi-squared test.
- Polymorphisms are the presence of different phenotypes existing in the same species in the same population. We are looking at distribution of polymorphic
- types based on environment, and how the distribution is related to gene flow, selection and genetic drift in the snail species Cepaea nemoralis.
However, after reviewing Jones' paper, we decided to study on determining solely whether the presence of polymorphisms in Cepaea nemoralis and environment-type had any visible correlation as a precursor to determining whether this implied selection was evident in this species, and if there was measurable gene-flow of the selected-for polymorphisms between populations in different habitats.Glossary of technical terms and their definitions:
Polymorphism - the occurrence of different forms among the members of a population or colony, or in the life cycle of an individual organism.
Subadult - an animal that is not fully an adult. Any snail that is a juvenile and doesn’t meet the size requirement to be classified as an adult is considered a subadult.
Genetic drift - the change in the frequency of a gene variant (allele) in a population due to random sampling.
Gene flow - the transfer of alleles or genes from one population to another. Migration into or out of a population may be responsible for a marked change in allele frequencies (the proportion of members carrying a particular variant of a gene).
Hypotheses:
Our null hypothesis is: There will be no correlation between the different environment type and polymorph types.
With the alternative being: There will be a correlation between different environment types and different polymorph types.
Reasoning:
As we are solely looking at distribution of snail polymorphisms between different environments, we are not testing for cause and effect - making testing
in the same environment multiple times less relevant. To reduce variables we are keeping our sampling locations on the same altitude along
a single transect. Our peripheral spots are completely within the given environment (forest and bush) with the following locations being just at
the periphery of this environment. The centre two are in between, completely outside of each environment, in grassland. This will construct a
gradient of samples between two separate locations.
Our original sample designs were as follows:
Sample Design 1.
Sample Design 2.
Reason for changes made
We felt there was not enough replication in the original design and it is not representative of the area as a whole, it leaves too much open
to chance as it covered only a small area of the habitat. Our original model would provide a more "in depth" view of the gradient of gene flow
as the sampling sites on the periphery and within each Wood and Bush area. We feel limited by the small number of sites that we will be able to
sample from in the time given so we have chosen to sample at a constant altitude across the entire area with replication in all three habitat types.
Sample Design 3.
Reason for changes made
First we decided to reduce the number of variables by only sampling 2 habitats and increasing repetition of the conditions of the measurements.
We hoped our investigation could compare phenotypes, grass samples are near forest samples, to investigate gene flow prevalence across the habitats.
Repetition of these conditions x3.
Justifying the method
Our method was to collect samples in two different habitats at sites which were close to each other where gene flow is possible. We did this because
we wanted to investigate the distribution across two different habitats to assess the possibility of gene flow having a considerable effect on the distribution
of polymorphisms. We replicated the samples three times for each habitat to produce a more representative sample size and reduce experimental error.